Electric device using solid electrolyte

ABSTRACT

The present invention relates to a transistor for selecting a storage cell and a switch using a solid electrolyte. In a storage cell, a metal is stacked on a drain diffusion layer of a field-effect transistor formed on a semiconductor substrate surface. The solid electrolyte using the metal as a carrier is stacked on the metal. The solid electrolyte contacts with the metal via a gap, and the metal is connected to a common grounding conductor. A source of the field-effect transistor is connected to a column address line, and a gate of the field-effect transistor is connected to a row address line.

TECHNICAL FIELD

The present invention mainly relates to an electric device using a solidelectrolyte. Particularly, the present invention relates to anonvolatile storage device which uses a solid electrolyte and whichenables to achieve high integration and high speed, and a method ofmanufacturing the device.

BACKGROUND ART

In a recent highly information-oriented society, a storage devicetemporarily or semipermanently holding a large amount of information hasbeen indispensable. Above all, a dynamic memory (DRAM), a flash memory,a read-only memory (ROM) and the like for use in a computer are wellknown.

A first related art is a flash memory. A storage cell of the flashmemory comprises one floating gate type transistor. A floating gateelectrode disposed between a channel region between source and drain anda control gate electrode is used as a storage node of information.

A charged state of the floating gate electrode is set in accordance with“0” and “1” of the information. Since the periphery of the floating gateelectrode is surrounded with an insulating film, the charge stored inthe electrode is not lost even after power cut-off, and therefore,nonvolatility is realized. A read operation is performed by using aproperty of a threshold voltage which changes in accordance with acharge amount stored in the floating gate electrode. A write/deleteoperation of the information is performed by injection of electrons intoa floating gate or release of the electrons from the floating gateelectrode by a tunnel current via an oxide film.

A second related art is a quantum point contact switch using anelectrochemical reaction in the solid electrolyte (refer to Riken ReviewNo. 37, p. 7, 2001). The solid electrolyte is a material in which ionsare freely movable in a solid as in a solution, and many materials thatexhibit conduction of cations or anions have heretofore been found. Whenan electric field is added, metal ions constituting carriers move in thesolid thereby to flow currents.

In the above-described document, a switch using silver sulfide which isa silver ion conductive solid electrolyte is described. The surface of asilver wire is sulfurated to form silver sulfide, and a platinum wire isbrought close to a micro gap. When a positive voltage is added to silversulfide, and a negative voltage is added to platinum, silver ions insilver sulfide are deposited as silver atoms on the surface, and abridge of silver is formed in the gap from platinum to form a pointcontact. The current hardly flows between silver sulfide and platinum incase where the bridge is not formed. When the bridge is formed, thecurrent flows.

The formation and disappearance of the bridge occur at a high rate whichis a microsecond or less. The current flowing in the bridge isquantized. The quantization of the current indicates that the bridge isformed of several atomic chains, and has a size of a nanometer order.With the use as the switch, a high-rate operation, low powerconsumption, and further high integration are possible. In the relatedart, it is described that application to the switch or memory results information of a new device.

The flash memory of the first related art is a device characterized by alow bit cost, and it is necessary to realize an advantage bit cost withrespect to another memory. In order to realize this, scaling of astorage cell is supposed to advance from now on. However, prospects arenot bright in the actual situation. One of causes for that lies in atunnel oxide film leak current generated with an increase of the numberof rewrites.

The leak current is a fatal phenomenon in which the charges stored inthe floating gate electrode are eliminated. Since the leak currentrapidly increases with the decrease of thickness of the oxide film, itis supposedly difficult to reduce the thickness of the tunnel oxidefilm. There arises a necessity for consideration of the scaling whichdoes not depend on the film thickness reduction.

In the second related art, upon forming the gap, use is made of a methodof using a scanning type tunnel microscope and a method of manuallybringing two metal wires close to each other. The method of using thescanning type tunnel microscope has an advantage that one gap can beformed with excellent controllability, but is not suitable for forming alarge number of gaps. The method in which the silver sulfide wires orthe platinum wires are manually brought close to each other isdeteriorated in controllability, and is similarly inappropriate forforming a large number of gaps. Furthermore, in silver sulfide on asilver wire as in the second related art, a size of one storage cell isof a millimeter order, and is not suitable for integration. Therefore,the integration of a storage device is impossible.

It is therefore an object of the present invention to provide a storagedevice using a solid electrolyte, particularly to a storage devicehaving a circuit constitution advantageous for integration and a methodof manufacturing the device.

DISCLOSURE OF THE INVENTION

The present invention is characterized by comprising a transistor forselecting a storage cell and a solid electrolyte switch (see FIG. 3(A)).In detail, the storage cell by a typical aspect of the present inventionis characterized in that a first metal thin film is stacked on a drainregion of a field-effect transistor formed on a semiconductor substratesurface, a solid electrolyte in which a metal ion of the first metalthin film is used as a carrier is stacked on the first metal thin film,the solid electrolyte intersects with a second metal thin film via a airgap, the second metal thin film is connected to a common groundingconductor, a source of the field-effect transistor is connected to acolumn address line, and a gate of the field-effect transistor isconnected to a row address line (see FIG. 3(B)).

According to another aspect of the present invention, the storage cellis characterized by comprising one diode and one solid electrolyteswitch (see FIG. 4(A)). In detail, the aspect is characterized in that afirst metal thin film is disposed on one electrode of a diode formed ona semiconductor substrate surface, a solid electrolyte in which a metalion of the first metal thin film is used as a carrier is disposed on thefirst metal thin film, a second metal thin film is disposed on the solidelectrolyte via an air gap, the second metal thin film is connected to arow address line, and the other electrode of the diode is connected tothe column address line (see FIG. 4(B)).

According to still another aspect of the present invention, one storagecell serving as an element of a storage device is characterized bycomprising one solid electrolyte switch (see FIG. 5(A)). In detail, theaspect is characterized in that a part of a first metal thin filmconnected to a row address line formed on a semiconductor substratesurface is a solid electrolyte using a metal ion of the first metal thinfilm as a carrier, and the solid electrolyte intersects with a secondmetal thin film connected to a column address line via an air gap (seeFIG. 5(B)).

Furthermore, a sacrificial layer needs to be used to form the air gapwith excellent controllability in order to highly integrate a solidelectrolyte switch. The sacrificial layer upon forming the air gap ischaracterized by the use of materials insoluble to a developing solutionof a photoresist and a solvent of the photoresist, such as acalixarene-based resist which is an electron beam resist, thermosettingresins such as polystyrene and polyimide, a silicon oxide film, and asilicon nitride film.

A solid electrolyte switch which is a constituting element of therepresentative aspect of the present invention is disposed on aninsulating film 52 on a semiconductor substrate 01 (FIG. 6(B)). A firstmetal thin film 53 is disposed on the insulating film 52, a solidelectrolyte 55 using the metal ion of the metal thin film as the carrieris disposed on the metal thin film 53, and further a second metal thinfilm 54 is disposed via an air gap 56. For a property of the switchusing the solid electrolyte, a current flowing in the second metal thinfilm 54 indicates a hysteresis at room temperature, when the first metalthin film 53 is grounded and a voltage added to the second metal thinfilm 54 is repeatedly increased/decreased in a predetermined range (FIG.6(A)).

As shown in FIG. 6(A), when the voltage applied to the second metal thinfilm 54 rises/lowers between a first voltage (−0.2 V) and a secondvoltage (0.5 V), the hysteresis appears in the current flowing in thesecond metal thin film 54 at room temperature. When the voltage isdecreased in a negative direction from 0 V, the current flows in thevicinity of −0.2 V. A resistance value is about 20 ohms. When thevoltage is swept in a positive direction, the current rapidly decreasesat +0.06 V. It is seen that a bistable state in which there is adifference of two or more digits in resistance can be realized between−0.2 and 0.06 V. It is seen that when the voltage is small, the bistablestate is held in (−0.2 to 0.06 V), and a latch function is realized. Ithas not heretofore been known that a switch operation and a latchoperation are performed in the solid electrolyte 55 on the first metalthin film 53, and this has experimentally been found by the presentinventors. In an experiment of FIG. 6A, the first metal thin film 53 isa silver thin film, the solid electrolyte 55 is a silver sulfide thinfilm, and the second metal 54 is platinum.

The above-described hysteresis property can be explained as follows withreference to FIG. 6(B).

When the first metal thin film 53 is grounded, and the negative voltageis added to the second metal thin film 54, electrons are supplied to thesolid electrolyte 55 from the second metal thin film 54 by a tunnelcurrent, and the metal ions are reduced on a solid electrolyte surfaceto deposit a metal 57. When the deposition is repeated, the air gap 56is narrowed, and finally a bridge is formed between the solidelectrolyte and the second metal thin film 54. At this time, the solidelectrolyte 55 is electrically connected to the second metal thin film54 so that the current flows. On the other hand, when the positivevoltage is added to the second metal thin film 54, the bridge of thedeposited metal 57 is oxidized, and diffused into the solid electrolyte55. When the oxidation is repeated, finally the air gap 56 is formed,and the solid electrolyte 55 is electrically disconnected from thesecond metal thin film 54.

From the above, it has been seen that the current can be turned on/offin one solid electrolyte switch. It is further seen that an on/off stateis held at a certain voltage or less, and the switch has the latchfunction. When the latch function is used, memory operations such aswrite, hold, and read of information are possible. The solid electrolyteswitch may have a size equal to an atomic size, and furtherminiaturization is possible as compared with a typical electric device.

The material insoluble to the organic solvent or the developing solutionof the photoresist is used in forming the air gap between the metal thinfilm and the solid electrolyte. For example, when the calixarene isexposed by the electron beam, molecules bond to each other to therebyform polymer having a large size. The polymer formed thus is a stablematerial which is insoluble to the solvent or the developing solution ofthe photoresist. On the other hand, since the material is organic, it iscarbonized by oxygen plasma treatments such as oxygen ashing, and can beremoved. As described above, it is possible to control the air gap inthe switch using the solid electrolyte with excellent controllability sothat a large number of devices can be integrated.

FIG. 14(A) shows a current/voltage property of the solid electrolyteswitch in which copper sulfide is used in the solid electrolyte 55,titanium is used in the second metal thin film 54, and copper is used inthe first metal thin film.

The voltages at which transition between the on-state and the off-stateof the solid electrolyte switch occurs are −1 V or more, 1 V or less,respectively. It is found out that when the voltage is applied to thesame solid electrolyte switch in a range of −3 to 5 V as shown in FIG.14(B), the voltage causing the transition of the on/off-state increases.

The on-state transits to the off-state at 3 V, and conversely theoff-state transits to the on-state at −3 V. The transition voltagechanges by movement of copper ions in the solid electrolyte, and thisrelates to spread of the above-described ion depletion layer. It has notheretofore been known that the transition voltage can be controlled bythe size of the applied voltage, and this has experimentally been foundby the present inventors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(A) is a diagram showing a solid electrolyte switch according to afirst embodiment of the present invention;

FIG. 1(B) is a diagram showing the solid electrolyte switch according toa second embodiment of the present invention;

FIG. 2 is a diagram showing a structure of a solid electrolytetransistor according to a third embodiment of the present invention;

FIG. 3(A) is a structural diagram showing a storage cell according to afourth embodiment of the present invention;

FIG. 3(B) is a circuit diagram showing a storage device using thestorage cell shown in FIG. 3(A);

FIG. 4(A) is a structural diagram showing the storage cell according toa fifth embodiment of the present invention;

FIG. 4(B) is a circuit diagram showing the storage device including thestorage cell shown in FIG. 4(A);

FIG. 4(C) is a diagram showing a modification of the storage cell shownin FIG. 4(A);

FIG. 5(A) is a structural diagram showing the storage cell according toa sixth embodiment of the present invention;

FIG. 5(B) is a circuit diagram showing the storage device including thestorage cell shown in FIG. 5(A);

FIG. 6(A) is a diagram showing a current/voltage property of the solidelectrolyte switch according to the present invention;

FIG. 6(B) is an explanatory view of a principle operation of the solidelectrolyte switch according to the present invention;

FIGS. 7(A), (B), (C), and (D) are explanatory views of a method ofpreparing the solid electrolyte switch shown in FIG. 1(A) in order ofsteps;

FIGS. 8(A), (B), (C), and (D) are explanatory views of the method ofpreparing the solid electrolyte switch shown in FIG. 1(B) in order ofsteps;

FIGS. 9(A), (B), (C), and (D) are explanatory views of the method ofpreparing the solid electrolyte transistor shown in FIG. 2 in order ofsteps;

FIGS. 10(A) and (B) are diagrams showing the solid electrolyte switchaccording to each embodiment of the present invention and the solidelectrolyte switch in a via hole;

FIG. 11 is a diagram showing FPGA of the present invention comprising alogic block, wiring, and solid electrolyte switch;

FIGS. 12(A), (B), (C), and (D) are is a sectional views showingrespective steps of a method of manufacturing the solid electrolyteswitch according to a seventh embodiment;

FIGS. 13 (A), (B), (C), and (D) are is a sectional views showingrespective steps of the method of manufacturing the solid electrolyteswitch according to an eighth embodiment; and

FIGS. 14(A), (B) are diagrams showing a method of controlling a voltagein the present invention, and showing a current/voltage property of thesolid electrolyte switch during changing of the voltage.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail withreference to the drawings.

First Embodiment

FIG. 1(A) shows a structural diagram of a solid electrolyte switch 10Ain accordance with the present embodiment.

The solid electrolyte switch 10A comprises a semiconductor substrate 01such as silicon. An insulating film 02 having a thickness of about 20angstroms to 200 angstroms is disposed on the semiconductor substrate01. The insulating film 02 may be an insulating film formed of a siliconoxide film, silicon nitride film, silicon oxynitride film, and the like.A first metal thin film 03 is disposed on the insulating film 02, and asolid electrolyte 05 using a metal ion which is a material of the firstmetal thin film 03 as a carrier is disposed on the first metal thin film03. The metal thin film 03 may be metals such as silver, and may have afilm thickness of 200 angstroms to 2000 angstroms. The solid electrolyte05 may be, for example, silver sulfide, and may have a film thickness of20 angstroms to 2000 angstroms. A second metal thin film 04 is disposedon the solid electrolyte 05 via an air gap 06.

As one example, a method of manufacturing the solid electrolyte switchwill be described with reference to FIGS. 7(A) to 7(D) in a case wherethe silicon oxide film is used in the insulating film 02, a silver thinfilm is used in the first metal thin film 03, silver sulfide is used inthe solid electrolyte 05, and platinum is used in the second metal thinfilm 04.

A silicon oxide film 62 having a film thickness of 300 nm is formed onthe silicon substrate 01 by a thermal oxidation method, and further thesilver thin film having a film thickness of 2500 angstroms is formed bya vacuum evaporation method or a sputtering method (FIG. 7(A)).

Thereafter, the film is processed in a thin wire by a wet etching methodor a reactive ion etching method. The thin wire may also be processed bya lift-off method. A silver thin film 63 is formed, and subsequentlysulfurated (FIG. 7(B)). There are two methods of sulfurating the silverthin film 63. In a first method of sulfuration, a silicon substratehaving the silver thin film 63 thereon is brought into a crucibletogether with a sulfur powder, and heated at 130 degrees in a bakefurnace in a nitrogen atmosphere. When conductivity of the silver thinfilm is measured during the sulfuration, the degree of the sulfurationcan be determined so that the silver thin film 63 can be sulfurated withexcellent control. The sulfuration is performed until the conductivitybecomes about ½.

In the second method of the sulfuration, the substrate is heated at 120degrees to 300 degrees in hydrogen sulfide diluted with nitrogen. Alsoin this case, when the resistance of the silver thin film 63 ismeasured, the sulfuration can be performed with excellent control. Bythe above sulfuration step, the surface of the silver thin film changesto black silver sulfide. Silver sulfide is a stable material existing innature, and is not deteriorated in the following steps, or notdeteriorated with an elapse of time.

Next, after the film is spin-coated with a calixarene resist, acalixarene resist 67 having a rectangular pattern is formed so as tocoat a part of silver sulfide 65 by an electron beam drawing device(FIG. 7(C)). After exposure, developing and rinsing are performed, andthereafter calixarene changes to a chemically stable polymer. Therefore,the resist is not dissolved in the solvent or developing solution of thephotoresist. The film thickness of calixarene can be adjusted bychanging a revolution number during the spin-coating and concentrationof calixarene. When 5 weight % of calixarene (solvent ismonochlorobenzene) is used, and a revolution number is 4000 rpm, thefilm thickness is 170 nm. It is possible to exactly adjust the filmthickness on the order of 10 nm.

Subsequently, a platinum thin film 64 is formed. After forming theplatinum thin film by the vacuum evaporation method or the sputteringmethod, the film is processed in the thin wire by the wet etching methodor the reactive ion etching method. The thin wire may also be processedby the lift-off method. A calixarene resist 67 formed on silver sulfideexists in a portion which overlaps with the silver sulfide 65, and thesilver sulfide 65 does not contact with the platinum thin film 64.

Finally, the calixarene resist 67 is removed by the oxygen ashing ororganic solvent (FIG. 7(D)). In the ashing, the organic material iscarbonized and consequently removed, and therefore the resist 67 canselectively be removed without damaging silver sulfide or platinum. Whenthe calixarene resist 67 is removed, an air gap 66 is formed betweensilver sulfide and platinum. The intervals of the air gaps can beadjusted by changing the film thickness of the calixarene resist 67.

An operation method of the solid electrolyte switch 10 will be explainedwith reference to FIG. 7(D).

When the silver thin film 63 is grounded, and a negative voltage (−0.2 Vor more) is applied to the platinum thin film 64, the switch turns on.On the other hand, when a positive voltage (0.06 V or more) is added tothe platinum thin film 64, the switch turns off. When the voltage is notapplied, or the applied voltage is small (−0.20 to 0.06 V), an on-stateor off-state is maintained.

In the above-mentioned embodiment, the calixarene resist 67 is removedto form the air gap 66, but the switching operation was confirmed evenin a such state that the calixarene resist 67 was left. It is supposedlybecause calixarene made of a soft material was pushed away to proceedwith silver deposition so that the bridge was formed upon forming thebridge of silver. Therefore, in case where the soft material is used asa sacrificial layer, the sacrificial layer is not always removed.

Second Embodiment

FIG. 1(B) shows a structural diagram of a solid electrolyte switch 10Bof another aspect of the present embodiment.

The solid electrolyte switch 10B comprises the semiconductor substrate01 such as silicon. The insulating film 02 having a thickness of about20 angstroms to 200 angstroms is disposed on the semiconductor substrate01. The insulating film 02 may be the insulating film formed of thesilicon oxide film, silicon nitride film, silicon oxynitride film andthe like. The second metal thin film 04 is disposed on the insulatingfilm 02, and the solid electrolyte 05 is disposed on the second metalthin film 04 via the air gap 06.

The second metal thin film 04 is, for example, the metal such asplatinum, and the film thickness may be 200 angstroms to 2000 angstroms.The solid electrolyte 05 is, for example, silver sulfide, and the filmthickness may be 20 angstrom to 2000 angstrom. The first metal thin film03 whose material is the metal ion as the carrier of the solidelectrolyte 05 is disposed on the solid electrolyte 05. When silversulfide is used as the solid electrolyte 05, the first metal thin film03 may be a silver thin film.

As one example, a method of manufacturing the solid electrolyte switchwill be described with reference to FIGS. 8(A) to 8(D) in a case wherethe silicon oxide film is used in the insulating film 02, the silverthin film is used in the first metal thin film 03, silver sulfide isused in the solid electrolyte 05, and platinum is used in the secondmetal thin film 04.

A silicon oxide film 72 having a film thickness of 300 nm is formed onthe silicon substrate 01 by the thermal oxidation method, and furtherthe platinum thin film having a film thickness of 2500 angstroms isformed by the vacuum evaporation method or the sputtering method (FIG.8(A)). Thereafter, the film is processed in the thin wire by the wetetching method or the reactive ion etching method. The thin wire mayalso be processed by the lift-off method.

Next, after the film is spin-coated with the calixarene resist, acalixarene resist 77 having the rectangular pattern is formed so as tocoat a part of a platinum thin film 74 by the electron beam drawingdevice (FIG. 8(B)). After the exposure, the developing and rinsing areperformed, and thereafter calixarene changes to the chemically stablepolymer. Therefore, the resist is not dissolved in the solvent or thedeveloping solution of the photoresist. The film thickness of calixarenecan be adjusted by changing the revolution number during thespin-coating and the concentration of calixarene. When 5 weight % ofcalixarene (solvent is monochlorobenzene) is used, and the revolutionnumber is 4000 rpm, the film thickness is 170 nm. It is possible toexactly adjust the film thickness on the order of 10 nm.

Subsequently, the silver thin film is formed, and sulfurated. There aretwo methods in sulfurating the silver thin film. In the first method ofsulfuration, the silicon substrate comprising the silver thin filmthereon is brought into the crucible together with the sulfur powder,and heated at 130 degrees in the bake furnace in the nitrogenatmosphere. In the second method of the sulfuration, the substrate isheated at 120 degrees to 300 degrees in hydrogen sulfide diluted withnitrogen.

By the above-mentioned step, the surface of the silver thin film changesto black silver sulfide. Silver sulfide is a stable material existing innature, and is not deteriorated in the following steps, or notdeteriorated with the elapse of time. As a result of sulfuration of thesilver thin film, a silver sulfide thin film 75 is formed (FIG. 8(C)).

Next, the calixarene resist 77 is removed by the oxygen ashing or theorganic solvent (FIG. 8(D)). In the ashing, the organic material iscarbonized and thereby removed, and therefore the resist 77 canselectively be removed without damaging silver sulfide or platinum. Whenthe calixarene resist 77 is removed, an air gap 76 is formed betweensilver sulfide and platinum. The intervals of the air gaps can beadjusted by changing the film thickness of the calixarene resist 77.Finally, a silver thin film 73 is formed on the silver sulfide thin film75 by the vacuum evaporation method or the sputtering method.

The operation method of the solid electrolyte switch 10 will beexplained with reference to FIG. 8(D).

When the silver thin film 73 is grounded, and the negative voltage (−0.2V or more) is added to the platinum thin film 74, the switch turns on.On the other hand, when the positive voltage (0.06 V or more) is addedto the platinum thin film 74, the switch turns off. When the voltage isnot applied, or the applied voltage is small (−0.2 to 0.05 V), theon-state or the off-state is maintained.

Third Embodiment

FIG. 2 is a structural diagram of a solid electrolyte transistor 20according to the present embodiment.

The solid electrolyte transistor 20 comprises the semiconductorsubstrate 01 such as silicon. An insulating film 12 having a thicknessof about 20 angstroms to 200 angstroms is disposed on the semiconductorsubstrate 01. The insulating film 12 may be an insulating film formed ofthe silicon oxide film, silicon nitride film, silicon oxynitride filmand the like. A metal thin film 13 is disposed on the insulating film12, and a solid electrolyte 15 using the metal ion which is the materialof the metal thin film 13 as the carrier is disposed in the metal thinfilm 13. The metal thin film 13 may be metals such as silver, and mayhave a film thickness of 200 angstroms to 2000 angstroms. The solidelectrolyte 15 may be, for example, silver sulfide, and may have a filmthickness of 20 angstroms to 2000 angstroms.

An insulating film 18 is disposed on the solid electrolyte 15, and agate electrode 17 is disposed on the insulating film 18. The insulatingfilm may be an insulating film having a thickness of about 20 angstromsto 200 angstroms and formed of the silicon oxide film, silicon nitridefilm, silicon oxynitride film and the like. A source electrode 11 and adrain electrode 14 are disposed on opposite ends of the metal thin film13. The source electrode, drain electrode, or gate electrode may be analuminum or metal thin film having a film thickness of 500 to 2000angstroms.

As one example, a method of manufacturing the solid electrolytetransistor will be described with reference to FIGS. 9(A) to 9(D) in acase where the silicon oxide film is used in the insulating film 12, thesilver thin film is used in the metal thin film 13, and silver sulfideis used in the solid electrolyte 15.

A silicon oxide film having a film thickness of 300 nm is formed on thesilicon substrate 01 such as silicon by the thermal oxidation method(FIG. 9(A)).

A silver thin film 83 having a film thickness of 2500 angstroms isformed by the vacuum evaporation method or the sputtering method, andfurther a source electrode 81 and a drain electrode 84 are formed by thevacuum evaporation method or the sputtering method (FIG. 9(B)).Thereafter, the sulfuration is performed (FIG. 9(C)). There are twomethods in sulfurating the silver thin film 83.

In the first method of sulfuration, the silicon substrate comprising thesilver thin film 83 thereon is brought into the crucible together withthe sulfur powder, and heated at 130 degrees in the bake furnace in thenitrogen atmosphere. There are two methods in sulfurating the silverthin film 83. In the first method of sulfuration, the silicon substratecomprising the silver thin film 83 thereon is brought into the crucibletogether with the sulfur powder, and heated at 130 degrees in the bakefurnace in the nitrogen atmosphere. When the conductivity of the silverthin film is measured during the sulfuration, the degree of thesulfuration can be determined, and the silver thin film 83 can besulfurated with excellent control. The sulfuration is performed untilthe conductivity becomes about 1/10.

In the second method of the sulfuration, the substrate is heated at 120degrees to 300 degrees in hydrogen sulfide diluted with nitrogen. Alsoin this case, when the resistance of the silver thin film 83 ismeasured, the sulfuration can be performed with excellent control. Bythe above-mentioned sulfuration step, the silver thin film changes toblack silver sulfide. Silver sulfide is a stable material existing innature, and is not deteriorated in the following steps, or notdeteriorated with the elapse of time. In the above-mentioned step, thesilver sulfide 75 is formed in the silver thin film 84.

Next, an insulating film 88 is formed (FIG. 9(D)). The insulating film88 may be an insulating film formed of the silicon oxide film, nitridesilicon film, silicon oxynitride film and the like, and is formed by avapor phase growth method or the like. The film thickness may be 20angstroms to 2000 angstroms. A gate electrode 87 is formed by usingaluminum as the material on the insulating film 88 by the sputteringmethod. The film thickness may be 500 angstroms to 2000 angstroms.

An operation method of the solid electrolyte transistor 20 will beexplained with reference to FIG. 9(D).

The source electrode 81 is grounded, and a micro positive voltage (about10 mV) is added to the drain electrode 84. When the negative voltage(about −1 V) is added to the gate electrode 87, a silver ion in thesilver thin film held between silver sulfide 85 and insulating film 82is attracted by the gate electrode, and moves in the silver sulfide 85.When silver moves, the air gap is generated, a current path to the drainelectrode 84 from the source electrode 81 is cut off so that thetransistor turns on. Conversely, when the positive voltage (about 1 V)is applied to the gate electrode 87, silver is deposited from the silversulfide 85 to thereby fill the air gap. In this event, the current pathis formed so that the transistor turns on.

Fourth Embodiment

FIG. 3(A) shows the structural diagram of a storage cell 100 accordingto the present embodiment, and FIG. 3(B) shows a circuit diagram of astorage device.

The storage cell 100 comprises the semiconductor substrate 01 such assilicon. A source region 110, a drain region 111 and a channel region109 disposed therebetween are formed in the substrate 01. A part of thesource region 110, the channel region 109, and a part of the drainregion 111 are coated with an insulating film 108 disposed to have athickness of about 20 angstroms to 200 angstroms. The insulating film108 may be an insulating film formed of the silicon oxide film, siliconnitride film, silicon oxynitride film and the like.

A source electrode 101 is disposed on the source region while a gateelectrode 107 is disposed on the insulating film 108. The material ofthe electrode may be metals such as aluminum, silver, and gold, orpolysilicon doped at a high concentration. A first metal thin film 103is disposed on the drain region 111, and a solid electrolyte 105 usingthe metal ion which is the material of the metal thin film 103 as thecarrier is disposed on the first metal thin film 103.

The metal thin film 103 may be metals such as silver, and the filmthickness may be 200 angstroms to 2000 angstroms. The solid electrolyte105 may be, for example, silver sulfide, and the film thickness may be200 angstroms to 2000 angstroms. A second metal thin film 104 isdisposed on the solid electrolyte 105 via an air gap 106.

The storage device is provided with a storage cell array 26 of thestorage cells 100. A peripheral circuit of the storage device includes acolumn address decode circuit 24 and a row address decode circuit 25which can be prepared by a related art. Connection to each storage cell100 with respect to the storage cell array 26 carried out as follows.

Specifically, all the second metal thin films 104 of the respectivestorage cells are connected to one another via a common groundingconductor 23, and grounded. The source electrodes 101 of the storagecells 100 in the same column are connected to one another via a columnaddress line. For example, a column address line 21 a is connected tothe source electrode 101 from each storage cell 100 in a left-endcolumn. The gate electrodes 107 of the respective storage cells 100 inthe same row are connected to one another via a row address line. Forexample, a row address line 22 a is connected to the gate electrode 107of each storage cell 100 in an upper-end row.

A method of manufacturing the above-mentioned storage device will bedescribed.

As one example, p-type silicon is used as the semiconductor substrate 01and channel region 109 while n-type silicon is used as the source region110 and drain region 111. Moreover, silver sulfide is used as the solidelectrolyte 105, and the platinum thin film is used as the second metalthin film 104. The column address decode circuit 24 or the row addressdecode circuit 25 as the peripheral circuit of the storage device can beproduced by the use of a semiconductor processing technique in a relatedart.

In the storage cell 100 constituting the storage cell array 26, thesource region 110, channel region 109, drain region 111, insulating film108, source electrode 101, and gate electrode 107 are produced by usingthe semiconductor processing technique in the related art.

Furthermore, the first metal thin film 103, solid electrolyte 105, airgap 106, and second metal thin film 104 are produced by using the methodof manufacturing the solid electrolyte switch 10 of the above-mentionedexample 1 shown in FIGS. 7(A) to 7(D).

Description will be made of the operation method of the present storagedevice produced by the above-described manufacturing method.

Operations such as write, delete (erase), and read are selectivelyperformed with respect to one specific storage cell in the storage cellarray 26. The storage cell may be selected by designating the rowaddress line and column address line connected to the storage cell to beselected. Here, a write state is defined as a case where the bridge isformed between the solid electrolyte 105 and the second metal thin film104 while a delete state is defined as a case where the bridge is notformed between the solid electrolyte 105 and second metal thin film 104.In order to write the storage cell 100 selected in the storage cellarray 26, the positive voltage (+1 V) is applied to the row address linerelated to the selected storage cell 100, and the positive voltage (+0.2V) is applied to the column address line related to the selected storagecell 100. At this time, in the selected storage cell 100, an n-channelis generated in the channel region 109 which is p-type silicon, thesource region 110 is electrically connected to the drain region 111, anda potential of the drain region 111 becomes substantially equal to thatof the source region 110.

In this manner, the positive voltage (about 0.2 V) is applied to thesolid electrolyte 105 of the selected storage cell so that a potentialdifference is caused between the solid electrolyte and the second metalthin film 104 connected to the common grounding conductor. By thepotential difference, the metal ion in the solid electrolyte isdeposited as the metal, and the bridge is formed between the solidelectrolyte and the second metal thin film 104. In order to delete theselected storage cell 100 in the storage cell array 26, the positivevoltage (+1 V) is applied to the row address line related to theselected storage cell 100, and the negative voltage (−0.2 V) is appliedto the column address line related to the selected storage cell. At thistime, the n-channel is generated in the channel region 109 which isp-type silicon, the source region 110 is electrically connected to thedrain region 111, and the potential of the drain region 110 becomessubstantially equal to that of the source region 111.

In this manner, the negative voltage (about −0.2 V) is applied to thesolid electrolyte 105 of the selected storage cell, and the potentialdifference is caused between the solid electrolyte and the second metalthin film 104 connected to the common grounding conductor. The metal ionforming the bridge moves into the solid electrolyte 105 by the potentialdifference, and the bridge disappears. In order to read the selectedstorage cell 100 in the storage cell array 26, the positive voltage (+1V) is applied to the column address line related to the selected storagecell 100, and the micro positive voltage (0.01 V) is applied to the rowaddress line related to the selected storage cell 100. At this time, then-channel is generated in the channel region 109 which is p-typesilicon, the source region 110 is electrically connected to the drainregion 111, and the potential of the drain region 111 is substantiallyequal to that of the source region 110.

In this manner, the positive voltage (about 0.01 V) is applied to thesolid electrolyte 105 of the selected storage cell 100, and thepotential difference is caused between the solid electrolyte and thesecond metal thin film 104 connected to the common grounding conductor23. The current flows into the column address line in a case where thebridge is formed (write state). On the other hand, the current does notflow in a case where the bridge is not formed (delete state). The stateof the storage cell 100 can be read by presence/absence of the current.

Fifth Embodiment

FIG. 4(A) shows the structural diagram of a storage cell 200 accordingto the present embodiment, and FIG. 4(B) shows a circuit diagram of thestorage device.

The storage cell 200 comprises the semiconductor substrate 01 such assilicon. The semiconductor substrate 01 is a p-type semiconductor. Ann-type semiconductor region 208 and p-type semiconductor region 207 aredisposed in the semiconductor substrate 01. An electrode 201 is disposedon the n-type semiconductor region 208. The material of the electrodemay be the metals such as aluminum, silver, and gold, or polysilicondoped at the high concentration.

A first metal thin film 203 is disposed on the p-type semiconductorregion 207, and a solid electrolyte 205 using the metal ion which is thematerial of the first metal thin film 203 as the carrier is disposed onthe first metal thin film 203. The first metal thin film 203 may be themetals such as silver, and the film thickness may be 200 angstroms to2000 angstroms. The solid electrolyte 205 may be, for example, silversulfide, and the film thickness may be 200 angstroms to 2000 angstroms.A second metal thin film 204 is disposed on the solid electrolyte 205via an air gap 206.

The storage device is provided with a storage cell array 36 of thestorage cells 200. The peripheral circuits of the storage device includea column address decode circuit 34 and a row address decode circuit 35which can be produced by the related art. The connection to each storagecell 200 in the storage cell array 36 is carried out as follows.Specifically, the electrodes 201 of the respective storage cells 200 inthe same column are connected to one another via the column addressline. For example, a column address line 31 a is connected to theelectrode 201 of each storage cell 200 in the left-end column. Thesecond metal thin films 204 of the respective storage cells 200 in thesame row are connected to one another via the row address line. Forexample, a row address line 32 a is connected to the second metal thinfilm 204 of each storage cell 200 in the upper-end row.

A method of manufacturing the present storage device will be explained.

As one example, p-type silicon is used as the semiconductor substrate 01while n-type silicon is used as the n-type semiconductor region 208.Moreover, p-type silicon is used as the p-type semiconductor region 207,silver sulfide is used as the solid electrolyte 205, and the platinumthin film is used as the second metal thin film 204. The column addressdecode circuit 34 and the row address decode circuit 35 as theperipheral circuit of the storage device can be produced by the use ofthe semiconductor processing technique in the related art.

In the storage cell 200 constituting the storage cell array 36, then-type semiconductor region 208, p-type semiconductor region 207, andelectrode 201 are produced by using the semiconductor processingtechnique in the related art. Furthermore, the first metal thin film203, solid electrolyte 205, air gap 206, and second metal thin film 204are produced by using the method of manufacturing the solid electrolyteswitch 10 of the present example 1 shown in FIGS. 7A to 7D.

In FIG. 4(A), the electrode 201 needs to be formed in a case where awiring resistance is lowered, but does not have to be necessarilyformed, when the n-type semiconductor region 208 is used as the wiringof the row address line. A degree of integration in this case may be asize of 2F×2F assuming a minimum processing line width F.

In the storage cell 200 of FIG. 4(A), when the p-type semiconductor 207and n-type semiconductor 208 are formed between the electrode 201 andthe first metal thin film 203 instead of being formed in thesemiconductor substrate, an area per one storage cell can be reduced(see FIG. 4(C)).

In detail, an insulating film 202 having a thickness of about 20angstroms to 200 angstroms is disposed on the semiconductor substrate01. The insulating film 202 may be an insulating film formed of siliconoxide film, silicon nitride film, silicon oxynitride film and the like.The electrode 201 is disposed on the insulating film 202. The materialof the electrode 201 may be the metals such as aluminum, silver, andgold, or polysilicon doped at the high concentration. The n-typesemiconductor region 208 is disposed on the electrode 201.

Further the p-type semiconductor region 207 is disposed on the n-typesemiconductor 208. The first metal thin film 203 is disposed on thep-type semiconductor region 207, and the solid electrolyte 205 using themetal ion which is the material of the first metal thin film 203 as thecarrier is disposed on the first metal thin film 203. The first metalthin film 203 may be the metals such as silver, and the film thicknessmay be 200 angstroms to 2000 angstroms. The solid electrolyte 205 is,for example, silver sulfide, and the film thickness may be 200 angstromsto 2000 angstroms. The second metal thin film 204 is disposed on thesolid electrolyte 205 via the air gap 206.

A method of manufacturing the storage cell of FIG. 4(C) will beexplained.

As one example, p-type silicon is used as the semiconductor substrate 01while n-type silicon is used as the n-type semiconductor region 208.Moreover, p-type silicon is used as the p-type semiconductor region 207,silver sulfide is used as the solid electrolyte 205, and the platinumthin film is used as the second metal thin film 204. The n-typesemiconductor region 208, p-type semiconductor region 207, and electrode201 are produced by using the semiconductor processing technique in therelated art. Furthermore, the first metal thin film 203, solidelectrolyte 205, air gap 206, and second metal thin film 204 areproduced by using the method of manufacturing the solid electrolyteswitch 10 of the present example 1 shown in FIG. 7(A) to 7(D).

Description will be made of the operation method of the present storagedevice produced by the above-described manufacturing method.

Operations such as write, delete, and read have to be selectivelyperformed with respect to one specific storage cell in the storage cellarray 36. The storage cell may be selected by designating the rowaddress line and column address line connected to the storage cell to beselected. Here, the write state is defined as the case where the bridgeis formed between the solid electrolyte 205 and the second metal thinfilm 204, and the delete state is defined as the case where the bridgeis not formed in the method of preparing the solid electrolyte switch205 and the second metal thin film 204.

In order to write the storage cell 200 selected in the storage cellarray 36, the positive voltage (+0.2 V) is applied to the row addressline related to the selected storage cell 200, and the negative voltage(−0.2 V) is applied to the column address line related to the selectedstorage cell 200. At this time, the potential difference is causedbetween the solid electrolyte 205 of the selected storage cell and thesolid electrolyte switch of the second metal thin film 204. Since apn-junction is formed in a boundary between the n-type semiconductorregion 208 and p-type semiconductor region, a reverse-direction voltageis added to the pn-junction in a case where the positive voltage isadded to the electrode 201. Therefore, the potential of the p-typesemiconductor region is determined by a relation between a pn-junctioncapacitance C1 and a capacitance C2 of the solid electrolyte 205 andsecond metal thin film 204. When C1 is substantially equal to C2, thepotential difference between the solid electrolyte 205 and the secondmetal thin film 204 is about 0.2 V. By the potential difference, themetal ion in the solid electrolyte is deposited as the metal so that thebridge is formed between the solid electrolyte and the second metal thinfilm 204.

Since only the potential difference of 0.1 V is caused between the solidelectrolyte 205 and the second metal thin film 204 related to thenon-selected storage cell, the bridge is not formed. Since the currentdoes not flow during the present write, power consumption is low. Inorder to delete the selected storage cell 200 in the storage cell array36, the negative voltage (−0.1 V) is applied to the row address linerelated to the selected storage cell 200, and the positive voltage (0.1V) is applied to the column address line related to the selected storagecell. At this time, the potential difference is caused between the solidelectrolyte 205 and the second metal thin film 204.

By this potential difference, the metal ion forming the bridge movesinto the solid electrolyte so that the bridge disappears. In order toread the selected storage cell 200 in the storage cell array 36, thenegative voltage (−0.01 V) is applied to the row address line related tothe selected storage cell 200, and the positive voltage (0.01 V) isapplied to the column address line related to the selected storage cell200. At this time, the potential difference is caused between the solidelectrolyte 205 and second metal thin film 204 of the selected storagecell 200. The current flows in the column address line in a case wherethe bridge is formed (write state). On the other hand, the current doesnot flow in a case where the bridge is not formed (delete state). Thestate of the storage cell 200 can be read by the presence/absence of thecurrent. There is a possibility that the current flows via the adjacentstorage cell, but either pn-junction in the current path has a reversedirection. Therefore, the current does not flow via the adjacent storagecell.

Sixth Embodiment

FIG. 5(A) shows the structural diagram of a storage cell 300 accordingto the present embodiment, and FIG. 5(B) shows a circuit diagram of thestorage device.

The storage cell 300 comprises the semiconductor substrate 01 such assilicon. An insulating film 302 having a thickness of about 20 angstromsto 200 angstroms is disposed on the semiconductor substrate 01. Theinsulating film 302 may be the insulating film formed of the siliconoxide film, silicon nitride film, silicon oxynitride film and the like.A first metal thin film 303 is disposed on the insulating film 302, anda solid electrolyte 305 using the metal ion which is the material of thefirst metal thin film 303 as the carrier is disposed on the first metalthin film 303.

The first metal thin film 303 may be the metals such as silver, and thefilm thickness may be 200 angstroms to 2000 angstroms. The solidelectrolyte 305 may be, for example, silver sulfide, and the filmthickness may be 200 angstroms to 2000 angstroms. A second metal thinfilm 304 is disposed on the solid electrolyte 305 via an air gap 306.

The storage device is provided with a storage cell array 46 of thestorage cells 300. The peripheral circuits of the storage device includea column address decode circuit 44 and a row address solid electrolytepreparation method decode circuit 45 which can be produced by therelated art. The connection to each storage cell 300 in the storage cellarray 46 is carried out as follows. Specifically, the first metal thinfilms 303 of the respective cells 300 in the same column are connectedto one another via the column address line. For example, a columnaddress line 41 a is connected to the first metal thin film 303 fromeach storage cell 300 in the left-end column. The second metal thinfilms 304 of the respective storage cells 200 in the same row areconnected to one another via the row address line. For example, a rowaddress line 42 a is connected to the second metal thin film 304 of eachstorage cell 300 in the upper-end row.

A method of manufacturing the present storage device will be explained.

As one example, silicon is used as the semiconductor substrate 01,silver sulfide is used as the solid electrolyte 305, and platinum isused as the second metal thin film 304. The column address decodecircuit 44 and the row address decode circuit 45 as the peripheralcircuits of the storage device can be produced by the use of thesemiconductor processing technique in the related art. The first metalthin film 303, solid electrolyte 305, air gap 306, and second metal thinfilm 304 of the storage cell 300 constituting the storage cell array 46are produced by using the method of manufacturing the solid electrolyteswitch 10 of the present example 1 shown in FIG. 7(A) to 7(D).

Description will be made of the operation method of the present storagedevice produced by the above-described manufacturing method.

Operations such as write, delete, and read have to be selectivelyperformed with respect to one specific storage cell in the storage cellarray 46. The storage cell may be selected by designating the rowaddress line and column address line connected to the storage cell to beselected. Here, the write state is defined as the case where the bridgeis formed between the solid electrolyte 305 and the second metal thinfilm 304, and the delete state is defined as the case where the bridgeis not formed in the solid electrolyte 305 and the second metal thinfilm 304.

In order to write the storage cell 300 selected in the storage cellarray 46, the negative voltage (−0.1 V) is applied to the row addressline related to the selected storage cell 300, and the positive voltage(+0.1 V) is applied to the column address line related to the selectedstorage cell 300. At this time, the potential difference is causedbetween the solid electrolyte 305 and the second metal thin film 304 ofthe selected storage cell. The potential difference between the solidelectrolyte 305 and the second metal thin film 304 is 0.2 V. By thepotential difference, the metal ion in the solid electrolyte isdeposited as the metal so that the bridge is formed between the solidelectrolyte and the second metal thin film 304.

Since only the potential difference of 0.1 V or less is generatedbetween the solid electrolyte 305 and the second metal thin film 304related to the non-selected storage cell, the bridge is not formed. Inorder to delete the selected storage cell 300 in the storage cell array46, the positive voltage (+0.05 V) is applied to the row address linerelated to the selected storage cell 300, and the negative voltage(−0.05 V) is applied to the column address line related to the selectedstorage cell. At this time, the potential difference is caused betweenthe solid electrolyte 305 and the second metal thin film 304. By thispotential difference, the metal ion forming the bridge moves into thesolid electrolyte so that the bridge disappears. In order to read theselected storage cell 300 in the storage cell array 46, the negativevoltage (−0.01 V) is applied to the row address line related to theselected storage cell 300, and an ion supply layer 507 can be omitted ina case where metal X is used in the selected first wiring layer 13. Thepositive voltage (0.01 V) is applied to the column address line relatedto the storage cell 300. At this time, the potential difference iscaused between the solid electrolyte 305 and second metal thin film 304of the selected storage cell 300.

The current flows in the column address line in a case where the bridgeis formed (write state). On the other hand, the current does not flow ina case where the bridge is not formed (delete state). There is apossibility that the current flows via the adjacent storage cell, but acurrent value is reduced by a certain resistance in the current path,and therefore it can be judged whether or not the current has flown viathe adjacent storage cell.

Seventh Embodiment

FIG. 10(A) shows a structural diagram of a solid electrolyte switch 500Aaccording to the present embodiment.

The solid electrolyte switch 500A is disposed on a substrate 501. Thesubstrate 501 has, for example, a structure in which the surface of thesilicon substrate is coated with an insulating layer. A first wiringlayer 503 is disposed on the substrate 501, and an ion supply layer 507is disposed on the first wiring layer 503. A solid electrolyte layer 506is disposed on the ion supply layer 507, and an interlayer insulatinglayer 502 is disposed so as to coat the substrate 501. A part of theinterlayer insulating layer 502 on the solid electrolyte layer 506 isopened to form a via hole, and an opposite electrode layer 505 isdisposed in the vicinity of the via hole through the solid electrolytelayer 506 and an air gap 508. Furthermore, a second wiring layer 504 isdisposed so as to coat the opposite electrode layer 505.

The solid electrolyte layer 506 is, for example, copper sulfide which isa compound conductor, and the film thickness may be 20 angstroms to 200angstroms. In the first wiring layer 503, copper having a film thicknessof 200 to 3000 angstroms is used. The material of the ion supply layer507 is the metal ion included in the solid electrolyte layer 506. Whencopper is used in the first wiring layer 503, the first wiring layer 503itself can be the ion supply layer, and therefore the ion supply layer507 may be omitted. When the first wiring layer 503 is other thancopper, copper is used as the material in the ion supply layer 507, andthe film thickness may be about 20 to 500 angstroms. In the secondwiring layer 504, copper having a film thickness of 200 to 3000angstroms is used. A size of the air gap 508 is about 10 angstroms to1000 angstroms.

When the solid electrolyte layer 506 is made of sulfides of metal Xother than copper, the ion supply layer 507 needs to be a materialcontaining the metal X. A combination of the solid electrolyte layer 506and ion supply layer 507 may be, in addition to copper sulfide-copperdescribed above, chromium sulfide-chromium, silver sulfide-silver,titanium sulfide-titanium, tungsten sulfide-tungsten, and nickelsulfide-nickel. Other than titanium described above, the oppositeelectrode layer 505 may contain platinum, aluminum, copper, tungsten,vanadium, niobium, chromium, molybdenum, or nitride, or silicide. Inaddition to copper described above, a wiring material which hasheretofore been used may also be used, and, for example, aluminum, goldand the like may also be used. When the metal X is used in the firstwiring layer 503, the ion supply layer 507 can be omitted.

One example of manufacturing steps will be described with reference toFIG. 12.

The silicon substrate is oxidized to produce the substrate 501. A copperthin film having a film thickness of 2000 angstroms is formed on thesubstrate 501 by the vacuum evaporation method or the sputtering method.Thereafter, a resist mask whose region other than the first wiring layer503 is opened is used, and the layer is processed in the form of thefirst wiring layer 503 by a wet etching method or reactive ion etchingmethod.

A resist pattern having an opening in a via hole 509 region is used as amask to sulfurate the opening. The sulfuration is performed by anodepolarization in an aqueous solution containing sulfide. A copper thinfilm is used as a cathode to perform the anode polarization in theaqueous solution containing 0.05 mol/liter of sodium sulfide. The addedvoltage is about 0.5 V, and a sulfide amount is adjusted by controllingthe current. Reaction is stopped where the copper thin film issulfurated by about 20 to 200 angstroms from the surface. A portionsulfurated to form copper sulfide forms the solid electrolyte layer 506while a non-sulfurated remaining copper portion forms the first wiringlayer 503. Since the material of the first wiring layer 503 is a metalconstituting the solid electrolyte, the ion supply layer 507 can beomitted.

There are two sulfuration methods other than the sulfuration method bythe above-described anode polarization. In the second method ofsulfuration, the substrate 501 comprising the copper thin film thereonis brought into the crucible together with the sulfur powder, and heatedat 130 degrees in the bake furnace in the nitrogen atmosphere. When theconductivity of the copper thin film is measured during the sulfuration,the degree of the sulfuration can be determined, and the copper thinfilm can be sulfurated with excellent control. The sulfuration isstopped where only the surface layer of the copper thin film issulfurated. In a third method of sulfuration, the substrate is heated at120 degrees to 300 degrees in hydrogen sulfide diluted with nitrogen.Also in this case, when the resistance of the copper thin film ismeasured, the sulfuration can be performed with excellent control. Bythis sulfuration step, the surface of the copper thin film changes tocopper sulfide. Moreover, instead of sulfurating the copper thin film toform copper sulfide, copper sulfide may also be deposited by thesputtering method or a laser abrasion method in the related art.

Next, a sacrificial layer 510 is formed in order to form the air gap508. Polymer which is decomposed at 400 degrees to 500 degrees is usedas the sacrificial layer 510. For example, a norbornene-based resinwhich is a thermosetting resin is used. The norbornene resin is appliedby the spin-coating, and a hardening treatment is performed. Instead ofthe norbornene-based resin, any polymer may be used that is insoluble tothe photoresist and that has thermal resistance and that is decomposedat about 500 degrees.

Thereafter, the resist mask whose region other than the via hole 509 isopened is used to process the norbornene resin in the form of the viahole 509 by the wet etching method or the reactive ion etching method.In this manner, the sacrificial layer 510 is formed. The size of thesacrificial layer 510 has to be larger than or equal to that of the viahole 509 region. Here, the structure shown in FIG. 12(A) can be formed.

Subsequently, the interlayer insulating layer 502 is formed. A siliconoxynitride film is formed by the sputtering method. After forming thefilm, the resist pattern whose via hole 509 region is opened is used asthe mask to form the via hole 509 by the dry etching or wet etching(FIG. 12(B)). The material of the interlayer insulating layer 502 ispreferably a low dielectric film, and a step of a low formationtemperature is low is desirable.

Next, the opposite electrode layer 505 is formed. Titanium is formed bythe vacuum evaporation method (FIG. 12(C)).

Then, copper is stacked by the sputtering method, and the resist maskwhich is opened except the region of the second wiring layer 504 is usedto form the second wiring layer 504 by a dry etching method. Finally,the temperature is raised at about 500 degrees to decompose thenorbornene-based resin so that the air gap is formed (FIG. 12(D)).

After producing the device, a voltage of ±4 V is applied to the solidelectrolyte layer 506 and the opposite electrode layer 505. Thus, anon-voltage of transition to the on-state from the off-state and anoff-voltage of transition to the off-state from the on-state are set toabout ±2 V. The setting of the voltage can appropriately be changed inaccordance with a use purpose.

Eighth Embodiment

FIG. 10(B) shows a structural diagram of a solid electrolyte switch 500Bby the present embodiment.

The solid electrolyte switch 500B is disposed on the substrate 501. Forthe substrate 501, for example, the surface of the silicon substrate iscoated with the insulating layer norbornene resin by the spin coating,and is hardened/treated. The first wiring layer 503 is disposed on thesubstrate 501, and the opposite electrode layer 505 is disposed on thefirst wiring layer 503. The interlayer insulating layer 502 is disposedso as to coat the opposite electrode layer 505 and substrate 501. A partof the interlayer insulating layer 502 on the opposite electrode layer505 is opened to form the via hole, and the solid electrolyte layer 506is disposed in the vicinity of the via hole through the oppositeelectrode layer 505 and air gap 508. Furthermore, the ion supply layer507 is disposed on the solid electrolyte layer 506, and the secondwiring layer 504 is disposed so as to coat the ion supply layer 507.

The solid electrolyte layer 506 is, for example, copper sulfide which isthe compound conductor, and the film thickness may be 20 angstroms to2000 angstroms. In the second wiring layer 504, copper having a filmthickness of 200 to 3000 angstroms is used. The material of the ionsupply layer 507 is the metal ion included in the solid electrolytelayer 506. When copper is used as the second wiring layer 504, thesecond wiring layer 504 is coated with the norbornene resin by the spincoating, and is hardened/treated. Since 504 itself can serve as the ionsupply layer, the ion supply layer 507 may be omitted.

When the second wiring layer 504 is other than copper, copper is used asthe material in the ion supply layer 507, and the film thickness may beabout 20 to 500 angstroms. In the second wiring layer 504, copper havinga film thickness of 200 to 3000 angstroms is used. The size of the airgap 508 is about 10 angstroms to 1000 angstroms.

When the solid electrolyte layer 506 is made of the sulfide of the metalX other than copper, the ion supply layer 507 needs to be the materialcontaining the metal X. The combination of the solid electrolyte layer506 and ion supply layer 507 may be, in addition to coppersulfide-copper described above, chromium sulfide-chromium, silversulfide-silver, titanium sulfide-titanium, tungsten sulfide-tungsten,and nickel sulfide-nickel. Other than titanium described above, theopposite electrode layer 505 may contain platinum, aluminum, copper,tungsten, vanadium, niobium, tantalum, chromium, molybdenum, or nitride,or silicide or 509.

In addition to copper described above, the wiring material which hasheretofore been used may also be used as the first wiring layer 503 andsecond wiring layer 504, and, for example, aluminum, gold and the likemay also be used. When the metal X is used as the second wiring layer504, the ion supply layer 507 can be omitted.

One example of the manufacturing steps will be described with referenceto FIG. 13.

The silicon substrate is oxidized to produce the substrate 501. Thecopper thin film having a film thickness of 2000 angstroms is formed onthe substrate 501 by the vacuum evaporation method or the sputteringmethod. Next, the opposite electrode layer 505 is formed. Titanium isformed by the vacuum evaporation method. The resist pattern having theopening in the region other than the first wiring layer 503 is used asthe mask to process the shape of the first wiring layer 503 by the wetetching method or the reactive ion etching method.

Then, the sacrificial layer 510 is formed in order to produce the airgap 508. Polymer which is decomposed at about 400 degrees to 500 degreesis used in the sacrificial layer 510. For example, the norbornene-basedresin which is the thermosetting resin is used. The norbornene resin isapplied by the spin-coating, and the hardening treatment is performed.Instead of the norbornene-based resin, any polymer may be used that isnot soluble to the photoresist and that has thermal resistance and thatis decomposed at about 500 degrees.

Thereafter, the resist mask whose region other than the via hole 509 isopened is used to process the norbornene resin in the form of the viahole 509 by the wet etching method or the reactive ion etching method sothat the sacrificial layer 510 is formed. The size of the sacrificiallayer 510 has to be larger than or equal to that of the via hole 509region. Here, the structure shown in FIG. 13(A) can be formed.

Subsequently, the interlayer insulating layer 502 is formed. The siliconoxynitride film is formed by the sputtering method. After forming thefilm, the resist pattern whose via hole 509 region is opened is used asthe mask to form the via hole 509 by the dry etching or wet etching(FIG. 13(B)). The material of the interlayer insulating layer 502 ispreferably the low dielectric film, and the step having the lowformation temperature is desirable.

Next, the solid electrolyte layer 506 is formed. The copper thin filmhaving a film thickness of 2000 angstroms is formed by the vacuumevaporation method or the sputtering method. Then, the sulfuration isperformed by the anode polarization in the sulfide-containing aqueoussolution. The copper thin film is used as the cathode to perform theanode polarization in the aqueous solution containing 0.05 mol/liter ofsodium sulfide. The added voltage is about 0.5 V so that the film iscompletely sulfurated.

There are two sulfuration methods other than the sulfuration method bythe above-described anode polarization. In the second method ofsulfuration, the substrate 501 comprising the copper thin film thereonis brought into the crucible together with the sulfur powder, and heatedat 130 degrees in the bake furnace in the nitrogen atmosphere. When theconductivity of the copper thin film is measured during the sulfuration,the degree of the sulfuration can be determined so that the copper thinfilm can be sulfurated with excellent control. The sulfuration isstopped where only the surface layer of the copper thin film issulfurated. In the third method of sulfuration, the substrate is heatedat 120 degrees to 300 degrees in hydrogen sulfide diluted with nitrogen.Also in this case, when the resistance of the copper thin film ismeasured, the sulfuration can be performed with excellent control.

Moreover, instead of sulfurating the copper thin film to form coppersulfide, copper sulfide may also be deposited by the sputtering methodor the laser abrasion method in the related art. The resist mask whichis opened except the region of the solid electrolyte layer 506 is usedto form the solid electrolyte layer 506 by the reactive ion etchingmethod (FIG. 13(C)).

Next, copper is stacked by the sputtering method, and the resist maskwhich is opened except the region of the second wiring layer 504 is usedto form the second wiring layer 504 by the reactive ion etching method.Since the second wiring layer 504 is copper, the production of the ionsupply layer 507 is omitted.

Finally, the temperature is raised at about 500 degrees so that thenorbornene resin is decomposed to form the air gap (FIG. 13(D)).

After producing the device, the voltage of ±4 V is applied to the solidelectrolyte layer 506 and the opposite electrode layer 505. In thismanner, the on-voltage of transition to the on-state from the off-state,and the off-voltage of the transition to the off-state from the on-stateare set to about ±2 V. The setting of the voltage can appropriately bechanged in accordance with the use purpose.

Ninth Embodiment

A switch mainly used in a field programmable gate array (FPGA) is ananti-fuse device. Since the resistance at an on-time is small, there isa characteristic that a signal delay is small, but re-programming isimpossible. During the programming of FPGA, debugging is impossible, andthe program cannot be switched during operation.

Even when the power is cut off, the solid electrolyte switch can holdthe on-state or the off-state. Furthermore, the resistance of theon-state is as small as several hundreds of Ω or less. From this reason,it is found out that the solid electrolyte switch is suitable for theswitch for connection and function selection of a logic circuit block ofFPGA. The anti-fuse device which has heretofore been used is notre-programmable, while the solid electrolyte switch is re-programmable10⁶ times. This is confirmed by the present inventor. The solidelectrolyte switch is structurally simple, and is operable with a sizewhich is approximately equal to an atomic size in principle. Therefore,further miniaturization is possible as compared with the conventionalelectric device.

FIG. 11 is a schematic diagram of the FPGA in which the solidelectrolyte switch according to the present embodiment is used.

A basic unit of FPGA comprises logic circuit blocks 601, wirings 602 to604, and solid electrolyte switches 605 which switch the connection ofthe wirings.

The logic block 601 and peripheral circuits are formed in the substrate01 of FIG. 1 or 2 or the substrate 601 of FIG. 10, and the solidelectrolyte switch described in any of the first and second and ninthembodiments is produced on the substrate 01 or 601.

INDUSTRIAL APPLICABILITY

According to the present invention, there is provided a storage deviceusing a solid electrolyte, and it is possible to especially provide astructure of a storage device having a circuit constitution advantageousfor integration, and a method of manufacturing the device.

1. An electric device which is a solid electrolyte switch and having alatch function, comprising: a first metal thin film that is disposed onan insulating film, the first metal thin film contacting with theinsulating film, a solid electrolyte that is disposed on a top surfaceof the first metal thin film, a metal ion of the first metal thin filmbeing used as a carrier in the solid electrolyte, and a second metalthin film that is disposed over the solid electrolyte and over the topsurface of the first metal thin film via an air gap, wherein the secondmetal thin film does not make contact with the solid electrolyte, andwherein the first metal thin film and the second metal thin film arepartially overlapped in a vertical direction with respect to theinsulating film.
 2. An electric device which is a solid electrolyteswitch and having a latch function, comprising: a solid electrolyte thatis disposed in a first part on a top surface of an insulating film; afirst metal thin film that is disposed on the solid electrolyte; and asecond metal thin film that is disposed on the top surface of theinsulating film, wherein the solid electrolyte is disposed in a secondpart over the second metal thin film via an air gap, wherein a metal ionas a carrier of the solid electrolyte being used as a material in thefirst metal thin film, wherein the second metal thin film does notcontact with the solid electrolyte, and wherein the first metal thinfilm and the second metal thin film are partially overlapped in avertical direction with respect to the insulating film.
 3. A storagedevice, comprising: one storage cell forming a constituting element ofthe storage device comprises (1) one field-effect transistor and (2) onesolid electrolyte switch according to claim 1 or 2, the solidelectrolyte switch according to claim 1 or 2 is disposed on a drainregion of the field-effect transistor formed on a semiconductorsubstrate surface, the second metal thin film of the solid electrolyteswitch is connected to a common grounding conductor, a source of thefield-effect transistor is connected to a column address line, and agate of the field-effect transistor is connected to a row address line.4. A storage device, comprising: one storage cell forming a constitutingelement of the storage device comprises (1) one diode and (2) one solidelectrolyte switch according to claim 1 or 2, the solid electrolyteswitch according to claim 1 or 2 is disposed on one electrode of a diodeformed on a semiconductor substrate surface, the second metal thin filmof the solid electrolyte switch is connected to row address line, andthe other electrode of the diode is connected to a column address line.5. A storage device, comprising: one storage cell forming a constitutingelement of the storage device and comprising the solid electrolyteswitch according to claim 1 or 2, a part of the first metal thin filmconnected to a row address line formed on a semiconductor substratesurface is the solid electrolyte in which a metal ion of the first metalthin film is used as a carrier, and the solid electrolyte intersectswith the second metal thin film connected to a column address line viathe air gap.
 6. An electric device, wherein: a semiconductor thin filmis disposed in a portion contacting with the gap in the second metalthin film according to claim 1 or 2, and a Schottky barrier is formed inan interface between a semiconductor and a metal so that a rectificationfunction operates, when the solid electrolyte switch turns on.
 7. Astorage device, wherein: a semiconductor thin film is disposed in aportion contacting with the gap in the second metal thin film accordingto claim 5, and a Schottky barrier is formed in an interface between asemiconductor and a metal so that a rectification function operates,when the solid electrolyte switch turns on.
 8. An electric deviceaccording to claim 1 or claim 2, wherein the solid electrolyte is anyone of silver ion conductive solid electrolytes, and copper ionconductive solid electrolytes, and a second metal is any one ofplatinum, tungsten, aluminum, gold, copper, and silver.
 9. A storagedevice according to claim 3, wherein the solid electrolyte is any one ofsilver ion conductive solid electrolytes, and copper ion conductivesolid electrolytes, and said second metal is any one of platinum,tungsten, aluminum, gold, copper, and silver.
 10. An electric device asthe solid electrolyte switch according to claim 1 or 2, wherein: avoltage is applied between a solid electrolyte layer and an oppositeelectrode layer at a manufacturing time in order to control anon-voltage which transits to an on-state from an off-state and anoff-voltage which transits to the off-state from the on-state.
 11. Anelectric device as a field programmable gate array comprising the solidelectrolyte switch according to claim 1 or 2, wherein: the solidelectrolyte switch is used as a first switch of wirings between logicblocks and a second switch which selects a function of the logic block.